fix: Enhance search sensitivity and add buyer to keyword filter

backend/app/routers/tenders.py

@@ -23,11 +23,13 @@ async def search_tender_opportunities(
     query = db.query(TenderModel)
     
     if keyword:
+        search_filter = f"%{keyword}%"
         query = query.filter(
             or_(
-                TenderModel.name.ilike(f"%{keyword}%"),
-                TenderModel.code.ilike(f"%{keyword}%"),
-                TenderModel.description.ilike(f"%{keyword}%")
+                TenderModel.name.ilike(search_filter),
+                TenderModel.code.ilike(search_filter),
+                TenderModel.description.ilike(search_filter),
+                TenderModel.buyer.ilike(search_filter)
             )
         )